Apparatus and method for preserving optical characteristics of a fiber optic device

ABSTRACT

An arrangement (apparatus and method) for hermetically sealing a fiber optic device to preserve its optical characteristics. The fiber optic device includes a device body such as an optical coupler or a multiplexer and optical fibers. Aluminum metal seals are formed on exposed regions of the optical fibers to provide an interface between the optical fibers and an enclosure. The metal seals may be formed directly on the optical fibers or by heating and compressing an aluminum sleeve onto an enclosure having an aluminum surface layer. The aluminum sleeve and surface layers melt and deform around the optical fibers, hermetically enclosing the fiber optic device.

CROSS REFERENCE TO RELATED APPLICATIONS

This is related to application Ser. No. 08/679,059, filed Jul. 12, 1996now U.S. Pat. No. 5,680,495.

CROSS REFERENCE TO RELATED APPLICATIONS

This is related to application Ser. No. 08/679,059, filed Jul. 12, 1996now U.S. Pat. No. 5,680,495.

TECHNICAL FIELD

The present invention relates to protecting fiber optic devices,specifically protecting fiber optic devices using metal.

BACKGROUND ART

Fiber optic devices need to be packaged to enable them to be used fortheir intended purpose. Packages generally include an inner supportstructure and an outer protective envelope. A fiber optic device can begenerally secured to the inner support structure by positioning thefiber optic device within the structure, for example a quartz body, andbonding the fiber optical device to the support structure with anadhesive such as UV light-curable epoxy. The outer protective envelope,for example a metal tube, is then assembled surrounding the supportstructure and the bonded device. The package is thus intended to protectthe device from environmental influences and damage.

The prior art packaging of fiber optic devices suffers from thefundamental problem that such packaging does not protect the physicalintegrity or the optical performance of the fiber optic device. Hence,prior art packaging never recognized that the optical characteristics ofa fiber optic device need to be preserved to ensure the long termperformance of a fiber optic device for its intended purpose.

DISCLOSURE OF THE INVENTION

There is a need for an arrangement (apparatus and method) for sealing afiber optic device in a manner that preserves the opticalcharacteristics of the fiber optic device.

There is also a need for an arrangement for preserving the opticalcharacteristics of a fiber optic device by physically protecting thefiber optic device from damage caused by environmental effects, forexample shock, deterioration due to exposure, etc.

There is also a need for preserving the optical characteristics of afiber optic device by preserving its operating environment.

There is also a need for preserving the optical characteristics of afiber optic device by preserving its mechanical state.

There is also a need for an arrangement for hermetically sealing a fiberoptic device to preserve its optical characteristics.

These and other needs are attained by the present invention, where metalseals that form a chemical and compressive seal with the optical fiberare used to preserve the optical characteristics of the fiber opticdevice within a sealed enclosure.

According to one aspect of the present invention, an apparatus includesa fiber optic device comprising at least one optical fiber having anexposed region, first and second metal seals surrounding the opticalfiber at first and second locations of the exposed regions, and a firstenclosure sealing the fiber optic device between the first and secondmetal seals. The first enclosure includes a first substrate having amiddle inner surface and end surfaces, the end surfaces contacting firstsurfaces of the first and second metal seals, respectively, and a secondsubstrate having a middle inner surface contacting the correspondingmiddle inner surface of the first substrate and end surfaces contactingsecond surfaces of the first and second metal seals, respectively. Themetal seals form a chemical and/or compressive seal on the opticalfiber, enabling the first enclosure to seal the fiber optic device in amanner that preserves the optical characteristics of the fiber opticdevice.

Another aspect of the present invention provides a method ofhermetically sealing a fiber optic device having at least one opticalfiber. The method comprises the steps of positioning the fiber opticdevice within first and second substrates, and heating and compressingmetal positioned between the first and second substrates onto an exposedportion of the optical fiber. The heated and compressed metal seals thefiber optic device within the first and second substrates, preservingthe optical characteristics of the fiber optic device.

Additional objects, advantages and novel features of the invention willbe set forth in part in the description which follows, and in part willbecome apparent to those skilled in the art upon examination of thefollowing or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and attained by means ofthe instrumentalities and combinations particularly pointed out in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the attached drawings, wherein elements having thesame reference numeral designations represent like elements throughout:

FIGS. 1A and 1B are diagrams of arrangements for hermetically sealing afiber optic coupler according to first and second embodiments of thepresent invention, respectively.

FIGS. 2A and 2B are diagrams illustrating side and top views of themetal blocks of FIG. 1A.

FIGS. 3A and 3B are diagrams illustrating top views of the molds used toform the metal blocks of FIG. 1A.

FIG. 4 is a diagram illustrating formation of the metal blocks of FIG.1A.

FIG. 5 is a perspective view of a substrate used to form the enclosureaccording to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating an upper and lower substrate forming aseal with a metal block according to a first embodiment of the presentinvention.

FIGS. 7A-7F are diagrams illustrating the sequence of hermeticallysealing the fiber optic device according to a first embodiment of thepresent invention.

FIG. 8 is a cross-section of the apparatus sealing the fiber opticdevice according to a first embodiment of the present invention.

FIGS. 9A-9I are diagrams illustrating the sequence of hermeticallysealing the fiber optic device according to a second embodiment of thepresent invention.

FIGS. 10A, 10B and 10C are diagrams of the substrate of FIG. 9Aaccording to a top plan view, a cross-sectional view along lines10b--10b, and a cross-sectional view along lines 10c--10c, respectively.

FIG. 11 is an exploded end view of the sealed enclosure of FIG. 9G.

FIG. 12 is a cross-section of the sealed enclosure along lines 12--12 ofFIG. 9G.

BEST MODE FOR CARRYING OUT THE INVENTION

Fiber optic devices are selected based on their manufactured opticalcharacteristics. Once manufactured, it is desirable to maintain theoptical characteristics of the fiber optic device to ensure the devicewill continue to operate as intended.

Different aspects of the fiber optic device may need to be protected topreserve the optical characteristics of the device. One aspect relatesto physically protecting the fiber optic device from damage. Such damagemay be due to environmental effects, including shock, deterioration dueto exposure, etc. Another aspect relates to preserving the operatingenvironment of the device itself. The optical characteristics of manyfiber optic devices are determined by their interaction with theirrespective operating environments. For example, a directional splitterhas a splitting ratio determined by the difference in the respectiverefractive indices of the waveguide and the operating environmentsurrounding the waveguide. Hence, the splitting ratio is preserved bymaintaining the refractive index of the surrounding operatingenvironment.

At the same time, it may be necessary to protect only certain aspects ofthe operating environment. Although the fiber optic device may bedesigned to measure an environmental condition by responding to anenvironmental stimulus according to a predetermined stimulus response,other optical, physical, or chemical influences may adversely affect theoperating environment, hence affecting the predetermined stimulusresponse of the device.

Still another aspect that may need to be protected to preserve theoptical characteristics of the fiber optic device relates to preservingthe mechanical state of the fiber optic device. The mechanical structureof the fiber optic device will contribute to its opticalcharacteristics. For example, a change in position of a waveguide in adirectional splitter may cause changes in forces in the waveguide, suchas stress. These changes may affect the optical characteristics in thedirectional splitter, such as the splitting ratio. Once the device ismanufactured with a desired optical characteristic, the physical stateof the device as manufactured needs to be preserved to maintain thedesired optical characteristic. This may include preserving the positionand static forces of the fiber optic device relative to its supportstructure.

The present invention enables all of the above-identified aspects to beprotected to preserve the optical characteristics of the device. Thefiber optic device may be an optical fiber coupler, a multiplexer, anattenuator, an optical switch, a laser diode, etc. As described below,the present invention preserves the optical characteristics of the fiberoptic device using metal seals formed on exposed regions of the opticalfibers. The metal seals bond to the optical fiber chemically andcompress on the optical fibers to form a hermetic seal. The metal sealsprovide an interface for substrate bodies used to enclose the fiberoptic device, where a hermetic seal is formed between the metal sealsand the substrates by compressing the substrates onto the metal seals.Hence, a fiber optic device may be sealed without the use of adhesives,enabling formation of a hermetic seal preserving the opticalcharacteristics of the optical fiber.

FIGS. 1A and 1B are diagrams illustrating apparatus for sealing a fiberoptic device according to first and second embodiments, respectively.The first and second embodiments each form metal seals on exposedportions of the optical fiber, providing an interface for the substratebodies to enclose the fiber optic device. The first embodiment isdirected to formation of metal blocks directly on the optical fiber,followed by compression of substrates onto the metal blocks to form agas-tight enclosure. The second embodiment uses metal blocks preformedwithin each substrate, where the substrates are heated and pressedtogether to seal the fiber optic device within a gas-tight enclosureformed by the sealed substrates.

As shown in FIG. 1A, the apparatus 40 includes a first movable stage 12and a second movable stage 14 that are independently movable along anaxis X. The stages 12 and 14 each include clamps 16 and 18 that are usedto secure optical fibers 20 and 22 to the stages 12 and 14. After theoptical fibers 20 and 22 are secured to the stages by the clamps 16 and18, the stages 12 and 14 are moved to position the fiber optic device 36into a desired state that provides the desired optical characteristic.Specifically, the desired optical characteristics of the fiber opticdevice 36 may be based on the operating environment of the device andthe mechanical state of the device. The operating environment may be aclean-room environment having an atmosphere consist of, for example, aninert gas such as argon at a predetermined pressure and having apredetermined refractive index. In addition, the stages 12 and 14 mayadd tension to the optical fibers 20 and 22 and twist the optical fibersas necessary.

As described below, the desired optical characteristics are preservedusing metal seals that preserve the mechanical state providing thedesired optical characteristic. Use of the metal seals in enclosing thefiber optic device also maintains the operating environment of the fiberoptic device, e.g., the predetermined refractive index, while at thesame time protecting the fiber optic device from environmental effectssuch as oxygen and water vapor that may degrade the fiber optic device.Depending on the application of the fiber optic device, the enclosureprotecting the fiber optic device may be implemented as a hermetic sealproviding a gas-tight seal.

The fiber optic device 36 includes optical fibers 20 and 22, each havingan exposed region 24, and a device body 28, for example a fiber opticcoupler, that is coupled to the optical fibers within the exposed region24. Although two optical fibers 20 and 22 are shown in FIG. 1A, a singleoptical fiber may be coupled to the fiber optic device 36, for example,if the fiber optic device 36 is an attenuator. The optical fibers arepreferably formed from fused silica, also known as fused quartz.

The method of hermetically sealing the fiber optic device 36 preferablyis initiated immediately after formation of the device body 28, althoughthe disclosed method is applicable to pre-existing fiber optic devicesthat are mounted on the apparatus 40 and have the optical fibers 20 and22 stripped to expose the optical fibers in the region 24. According tothe disclosed embodiment, the exposed region 24 has a length ofapproximately 40 to 66 millimeters.

As shown in FIG. 1A, the apparatus 40 includes mold portions 42 that arepositioned at first and second locations of the exposed region 24 toform metal blocks 44 for hermetically sealing the device 36 according tothe first embodiment. Specifically, the molds 42a and 42b arecomplementary molds that are moved to enclose the optical fibers 20 and22. As described below, the molds 42a and 42b are used to form the metalblock 44a. Similarly, the molds 42c and 42d are moved together toenclose the fibers 20 and 22, in order to form the metal block 44b.Although not shown in FIG. 1A, additional components may be pre-threadedonto the optical fibers 20 and 22 between the mounts 16 and 18.Alternatively, one of the mounts may be temporarily opened to addcomponents threaded on the fiber, described below.

FIGS. 2A and 2B are side and top views of the metal blocks 44 of FIG.1A, respectively. The metal block 44, also referred to as a metal seal,includes metal extensions 46 that provide strain relief for the opticalfibers and a cubic portion 48 that serves as a support structure forenclosures to be added to the assembly, described below. The extensions46 thus provide structural strength preventing the optical fibers 20 and22 from bending on an edge. Although disclosed as a cubic structure, theportion 48 of the metal block 44 may have other shapes.

FIGS. 3A and 3B are diagrams illustrating the inner views of the molds42a and 42b, respectively. As shown in FIG. 3A, the mold 42a includes acavity 50 used to form the portion 48 of the metal seal 44. The mold 42aalso includes notches 52 that are used to form the extensions 46. Themold 42a also includes a surface 54a that comes into contact with thecorresponding surface 54b of the complementary mold 42b, and an aperture56 for evacuating atmosphere and injecting inert gas and molten metal.The complementary mold 42b includes a corresponding cavity 50bcomplementary to the cavity 50a to form the cube portion 48, andportions 52b complementary to the portions 52a that form the extensions46. The mold 42b also includes on the surface 54b a mold seal 56surrounding the outer edge of the surface 54b. The mold seal, preferablya high-temperature polymer seal, forms a tight seal with the moldportion 42a to ensure an airtight fit between the molds 42a and 42bduring enclosure of the fibers 20 and 22. Hence, the aperture portions52a and 52b enclose the optical fibers 20 and 22 to form a tight fit,preventing any leakage of molten metal or any gas.

FIG. 4 is a diagram illustrating operation of the molds 42 to form themetal seal 44 on the optical fibers. The molds 42a and 42b are movedtogether to enclose the optical fibers 20 and 22 to form an airtightregion for forming the metal seal 44. The region includes the cavity 50and the region 52. After the molds 42a and 42b are secured around theoptical fibers 20 and 22, the atmosphere is evacuated from the cavity 50via the aperture 56. The overall procedure of forming the fiber opticdevice 36 and hermetically sealing the fiber optic device is performedin a predetermined oxygen-free operating environment.

After the oxygen-free environment has been evacuated from the chamber50, an inert gas, for example argon, helium or nitrogen is flooded intothe cavity 50 at a positive pressure relative to the atmosphere viaaperture 56. After the region 50 has been flooded with the inert gas, avacuum is generated in the cavity 50 by evacuating the inert gas. Once asufficient vacuum has been formed in the cavity 50, molten metal isinjected into the cavity 50 at a temperature slightly above the meltingpoint of the molten metal. According to the disclosed embodiment, themolten metal preferably consists essentially of oxygen-free, pure liquidaluminum. Hence, the pure liquid aluminum is injected into the cavity 50via aperture 56 at a temperature slightly above the melting point ofpure aluminum, for example 700° C.

According to the disclosed embodiment, aluminum has a relatively highmelting point, and will bond to the fused silica optical fibers 20 and22. Hence, the pure liquid aluminum injected at slightly above 660° C.will bond to oxygen molecules on the surface of the optical fibers 20and 22 without devitrifying the optical fibers (i.e., breaking down theglass state). The molds 42 include an ultrasonic transducer 60 thatapplies ultrasonic energy to the molds 42. The ultrasonic transducers 60reduce the surface energy of the liquid aluminum, reducing the surfacetension so that the aluminum wets better to the optical fibers 20 and22. The molds 42 are formed of ceramic to ensure that the aluminum doesnot easily wet to the molds 42. In addition, the ceramic material hasappropriate thermal characteristics to cool the liquid aluminum to asolid state after a few seconds after injection. After sufficientcooling of the aluminum into a solid state, the molds 42A and 42B may beretracted from the optical fibers 20 and 22, resulting in completedformation of the metal blocks 44 as shown in FIG. 1A and FIG. 7B. Ifdesired, the ultrasonic transducers 60 may be operated continuouslythroughout the injection process to ensure the aluminum does not wet tothe molds.

A particular advantage of the disclosed embodiment is that the liquidaluminum chemically bonds with the fibers 20 and 22 to form a gas-tightseal. In addition, the aluminum liquid tends to compress during cooling.Hence, the cooled aluminum block 44 forms a hermetic seal with theenclosed optical fibers by forming a chemical bond with the opticalfibers and by exerting compressive forces on the fibers. The metalblocks 44 also provide a fixed frame of reference with respect to thecoupler 28. Specifically, the metal blocks 44 secure the optical fibersin a static state to preserve the mechanical state of the device asdescribed above.

After formation of the metal blocks 44, the assembly including theoptical fibers 20 and 22, the coupler 28, and the metal blocks 44 areenclosed within quartz enclosures while secured to the mounts 16 and 18.If necessary, however, the assembly may be moved as desired whilemaintaining a fixed frame of reference with respect to the coupler 28.Hence, the fiber optic device 36 may be moved for manufacturing ortesting purposes without adversely affecting the precise alignmentrequirements associated with fiber optic assembly. The blocks 44 maythen be used to secure the assembly to another mounting assembly forcompleting the sealing process, described below.

The fiber optic device 36 is hermetically sealed by enclosing the fiberoptic device 36 and at least portions of the metal seals 44a and 44bwithin an enclosure 62, shown in FIG. 7C. The enclosure 62 includes afirst substrate 64a and second substrate 64b that are positioned on themetal seals 44a and 44b in an atmosphere defining the preferredoperating environment of the fiber optic device. According to thedisclosed embodiments, the enclosure 62 is formed in an inertatmosphere, such as nitrogen, helium or argon, that has a predeterminedrefractive index. The inert atmosphere is preferably at a predeterminedpressure greater than ambient air pressure. Hence, formation of theenclosure 62 in the specified atmosphere ensures that the completedenclosure 62 preserves the operating environment of the fiber opticdevice by sealing the device within a positive-pressure inertatmosphere. The enclosure 62 also protects the fiber optic device 36from environmental contaminants such as oxygen or water vapor.

FIG. 5 is a perspective view of the substrate 64. As shown in FIG. 5,the substrate 64 includes a trough 66 extending axially along thesubstrate 64. The trough 66 is designed to accommodate the opticalfibers 20 and 22 and the device body 28. The substrate 64 has endregions 68 adapted to engage one of the metal seals 44. For example, theend 68a engages the bottom surface of the metal seal 44a, and the end68b engages the bottom surface of the metal seal 44b. The substrate 64aincludes similar ends that engage the upper surface of the metal seals44, as shown in FIG. 6. Each substrate 64a and 64b includes a deformablemetal layer used to seal the substrate 64 with the correspondingcontacting surface. For example, FIG. 5 illustrates that each end 68includes a deformable metal layer 70. In addition, the middle surfaces72 of the substrate 64 also include the deformable metal layer 70.

FIG. 6 is a cross-sectional diagram of an end of the substrate 64 inrelationship to a metal seal 44 that encloses the optical fibers 20 and22. Each substrate 64a and 64b includes a body 74 and a deformable metallayer 70 overlying the body 74. According to the first disclosedembodiment, the body 74 consists essentially of fused silica, and thedeformable metal layer 70 comprises a first layer 76 and a second layer78. According to the disclosed embodiment, the first metal layer 76consists essentially of pure aluminum, and the second metal layer 78consists essentially of gold. If desired, however, the second metallayer 78 can be eliminated such that the deformable metal layer 70 isformed only of the first aluminum layer 76.

As shown in FIG. 6, the substrates 64a and 64b each have a trough 66having a width W₁, that is less than the width W₂ of the metal seal 44.Each of the substrates 64 also have a height H₁ that is less thanone-half the height of the metal block 44, H₂. Hence, the dimensions ofthe troughs 66a and 66b require the interface metal layer 70 to deformin order to accommodate the metal seal 44. Hence, the metal layers 70within the trough 66 at the end regions is deformed as the metal seal 44is pressed into the trough 66 during the compression of the substrates64a and 64b onto the metal block 44. Hence, the compression of thesubstrates 64a and 64b onto the metal seal 44 causes the metal seal 44to be securely fitted into the trough 66, creating a hermetic seal bythe displacement of the deformable metal layer 70 around the block 44.In addition, the metal block 44 may also be partially deformed duringthe compression process. Finally, compression of the substrates 64a and64b causes the compression of the metal layers 70 at the complementarymiddle regions 72, creating a hermetic seal between the substrates 64aand 64b along the middle surface 72. If desired, ultrasonic welding mayalso be performed to weld the contacting metal layers.

After the substrates 64a and 64b have been compressed onto the metalseal 44, the compressed substrates 64 and the metal blocks 44 form anenclosure 62, shown in FIG. 7C, having a gas-tight seal around thedevice body 28 that maintains the optical characteristics of the fiberoptic device by preserving the desired operating environment. Thegas-tight seal also protects against environmental contaminants. Theenclosure 62 also maintains the optical characteristics of the fiberoptic device by physically protecting the device from damage from shock,impact, etc. The enclosure 62 also maintains the physical state of thefiber optic device by preserving the physical orientation and the staticforces within the fiber optic device. Hence, any static forces necessaryfor the fiber optic device to operate according to a prescribed response(e.g., fiber tension, fiber twisting) can be maintained by the metalblocks 44 secured with respect to the substrates 64.

After formation of the enclosure 62, a tubing 80 is threaded over theenclosure 62, shown in FIG. 7D. The tubing 80, formed of fused silica,includes a deformable metal interface layer, such as the aluminum/goldinterface layer 70 as described above, on at least the inner surface ofthe tube. The tube 80 has an inner diameter which is slightly less thanthe outer diameter of the enclosure 62. Hence, the deformable metalinterface layer on the inner surface of the tubing 80 interacts with thedeformable interface layer on the outer surface of the enclosure 62 toform a second gas-tight enclosure exerting a compressive force on theenclosure 62. The compressive force by the tubing 80 provides additionalsealing between the tubing 80 and the substrates 64a and 64b of theenclosure 62, and maintains the hermetic seal between the substrates 64aand 64b and the metal blocks 44. In addition, the tubing 80 hermeticallyseals the enclosure 62 within the second gas-tight enclosure, protectingthe enclosure 62 from long term environmental effects and maintainingthe integrity of the first hermetic seal established by the enclosure62. Finally, the use of fused quartz for the substrates 64 and thetubing 80 ensures that the thermal expansion coefficients of theenclosures match the fiber optic device. Hence, uniform expansion of thefiber optic device, the optical fibers, the substrates 64 and the tubing80 preserves the mechanical state of the fiber optic device. Theexpansion coefficient and ductile nature of the metal seals issufficient to accommodate the preservation of the mechanical stateduring thermal expansion.

Ultrasonic welding may also be used to seal the contacting metal layers.If desired, two ultrasonic welding steps may be performed, first duringformation of the enclosure 62, and after threading the tubing 80 overthe enclosure 62. Alternatively, a single ultrasonic welding may beperformed after the threading of the tubing 80 over the enclosure 62.Other types of welding may also be used to fuse the metal layerstogether.

After sealing the tubing 80 as shown in FIG. 7D, gold caps 82 are addedonto each end of the tubing 80 in FIG. 7E to cover the ends of thetubing 80, and the ends of the metal seals 44. The caps 82 may beprethreaded on the optical fibers 20 and 22, or may be attached bycrimping a sheet of gold metal at each end. As the gold caps 82 arecompressed and ultrasonically welded at each end of the tubing 80, theportions of the metal seal 44 extending from the tubing 80 are partiallydeformed with the caps 82. After the gold caps 82 have been secured onthe ends of the tubing 80, the exposed optical fibers are coated with aconventional sealing material 84, for example rubber or UV-curedacrylate. The sealing material 84 coating the gold caps 82 and thecoating 85 also provides stress and strain protection for the opticalfibers by transferring forces on the coating 85 to the gold caps 82instead of the optical fibers. Hence, the gold caps 82 and sealingmaterial 84 provide additional protection for the fiber optic devicefrom external shock.

After the exposed optical fibers have been covered by the sealant 84, aprotective metal tubing 86, formed of a nickel-based alloy, for exampleInvar, is threaded over the assembly. If desired, a nonmetal tubinghaving relatively low thermal expansion coefficient may also be used.After loosely fitting the metal tubing 86 over the assembly, the metaltubing 86 is secured by injecting into the space between the tubing 86and the assembly a sealant, for example an RTV (room temperaturevulcanizing) silicon coating 88. Once the RTV 88 has hardened, thecompleted assembly 100 shown in FIG. 7F may be packaged.

FIG. 8 is a cross-section of the apparatus sealing the fiber opticdevice along lines I--I of FIG. 7F. As shown in FIG. 8, the opticalfibers 20, 22 connected to the fiber optic device (not shown) aresupported in a desired mechanical state within the enclosure 66 by themetal seals 44. The optical fibers are also hermetically sealed in agas-tight enclosure 66 formed by the troughs and enclosing the desiredoperating environment, for example an inert gas at a positive pressurerelative to ambient air pressure. The enclosure 66 is bounded by thequartz bodies 74 and the deformable metal layer 70. The quartz tubing 80provides additional compressive forces on the enclosure 62 to maintainthe compressive seal. Hence, even though the RTV coating 88 may besusceptible to moisture, the compressive force exerted by the quartztubing 80 hermetically seals the enclosure formed by the metal seals andquartz substrates 64a and 64b. Hence, the hermetic seal between thequartz substrates 64a and 64b, and the metal seals 44a and 44b isprotected from environmental effects.

The second embodiment of the present invention uses metal blocks 44a and44b that are initially formed on the quartz substrates to form anenclosure that preserves the optical characteristics of the fiber opticdevice.

FIGS. 9A-9G summarize the sequence of hermetically sealing the fiberoptic device 28 within an enclosure according to the second embodiment.As shown in FIG. 9A, the fiber optic device 28 is positioned between afirst substrate 204a and second substrate 204b to form an enclosure 200,shown in FIG. 9B.

FIG. 10A is a top plan view of substrate 204, and FIGS. 10B and 10C arecross-sectional views of the middle and end portions of the substrate204, respectively.

As shown in FIGS. 10A and 10B, the substrate 204 includes a trough 212,extending axially along the substrate 204, that accommodates the opticalfibers 20 and 22 and the device body 28. As shown in FIG. 10C, endregions 214a and 214b of the substrate 204 have respective metal blocks215a and 215b adapted to surround the optical fibers 20 and 22. Eachmetal block 215 includes slots 217 to accommodate the exposed region 24of optical fibers 20, 22. As shown in FIG. 9A, substrate 204 has taperedportions 220 at its distal ends.

The substrate 204 includes a quartz body 222 having a flat surface 226and a metal layer 224 overlying at least the surface 226. Another metallayer 224' overlays at least the outside surfaces of end regions 214a,214b. The quartz body 222 may consist essentially of fused silica, andthe metal layers 224 and 224' overlying the quartz body 222 may consistessentially of pure aluminum.

The method of sealing the fiber optic device 28 to preserve its desiredoptical characteristics according to the second embodiment will now bedescribed with respect to FIGS. 1B and 9A-9I. FIG. 1B is a diagram of anapparatus 210 for hermetically sealing the fiber optic device 28 topreserve its desired optical characteristics according to the secondembodiment. As shown in FIG. 9A, the fiber optic device is positionedbetween substrate 204a and 204b and the substrates 204a and 204b aremoved together using support members (not shown), forming enclosure 200as illustrated in FIG. 9B.

As shown in FIG. 1B, the apparatus 210 includes a pair of hollow endrods 232. The optical fibers 20, 22 are previously threaded through theend rods 232. The end rods 232 are moved to engage the end portions 214aand 214b to align and hold substrates 204a and 204b as shown in FIG. 9C.

A sleeve 234 consisting essentially of pure aluminum is then threadedover enclosure 200 as depicted in FIG. 9D. Sleeve 234 has an innerdiameter slightly greater than the outer diameter of enclosure 200 and,as depicted, a length slightly greater than enclosure 202.

As shown in FIG. 9E, an upper mold member 242 and a lower mold member244, part of the closing apparatus 210 of FIG. 1B, engage the sleeve234. The mold members 242 and 244 can include heating elements or anultrasonic transducer, or alternatively, a separate heater can beincluded as part of closing apparatus 210. The apparatus 210 exertssufficient pressure on the sleeve 234 to keep the sleeve 234 and theenclosure 202 together as a unit and in alignment as the end rods 232are moved apart as shown in FIG. 9F.

The upper and lower mold members 242, 244 heat the sleeve 234 and metalwithin the substrates 204 to fuse the metal together. Specifically, themold members 242, 244 heat the sleeve 234, the metal blocks 215 and themetal layers 224 and 224' to just below their melting points. The moldmembers then compress the sleeve 234 and the substrates 204a and 204btogether, causing the metal blocks 215 and the metal layer 224 of thesubstrate 204a to fuse with the corresponding metal block 215 and metallayer 224 of the substrate 204b. The metal blocks 215 surrounding theoptical fibers 20, 22 also hermetically seal the optical fibers as themetal blocks are fused together by bonding with the oxygen moleculeswithin the optical fibers and compressing on the optical fibers as themetal blocks shrink during cooling. Hence, the fusion of the metalblocks 215 and the metal layers 224 hermetically seal optical fibers 20,22 within the substrates 204a and 204b to seal the enclosure 200. Inaddition, the sleeve 234 fuses with the outer metal surface 224' of thesealed enclosure 200 to hermetically encapsulate the enclosure 200 withan additional hermetic (gas-tight) seal, forming the hermetic enclosure260 of FIG. 9G.

FIG. 12 is a cross section of the hermetic enclosure 260 of FIG. 9Galong lines 12--12. The fiber optic device 28 is supported by the fusedmetal blocks 215 (not shown) to be suspended within the trough 212 ofthe quartz bodies 222, preserving the desired operating environment ofthe fiber optic device 28. The quartz bodies and the fiber optic device28 are sealed within the metal seals, including the metal surfaces 224and the fused seal 261 formed between the outer metal surfaces 224' andthe sleeve 234. Hence, the fused seal 261 hermetically seals both thefiber optic device 28 and the enclosure formed by the quartz bodies 222,ensuring long-term protection of the device 28.

After hermetic enclosure 260 is formed, the exposed optical fibers 20,22 are coated with the conventional sealing material 84, for example RTVas depicted in FIG. 9H.

After the exposed optical fibers have been covered by the sealant 84, aprotective metal tubing 86, formed of a nickel-based alloy, for exampleInvar, is threaded over the assembly as depicted in FIG. 9I. If desired,a nonmetal tubing having a relatively low coefficient of thermalexpansion may also be used. After loosely fitting the metal tubing 86over the assembly, the metal tubing 86 is secured by injecting into thespace between the tubing 86 and the assembly a sealant, for example anRTV (room temperature vulcanizing) silicon coating 88. Once the RTV 88has hardened, the completed assembly 270 shown in FIG. 9I may bepackaged by coating the ends of the optical fibers as necessary.

Hence, the optical fibers 20, 22 are hermetically sealed in a gas-tightenclosure 260 that encloses the desired operating environment of thefiber optic device, bounded by the quartz bodies 204a, 204b and metallayer 224. The sleeve 234 provides additional compressive forces on theenclosure 260 to maintain the compressive seal. In addition, the sleeve234 provides its own protection of the quartz bodies 204, providing agas-tight seal that protects the quartz bodies 204. Hence, even thoughthe RTV coating 88 may be susceptible to moisture, the long-termintegrity of the quartz bodies enclosing the fiber optic device ismaintained.

According to the present invention, the optical characteristics of afiber optic device are preserved using metal seals that form a chemicaland compressive seal on optical fibers. The metal seals also form acompressive seal between the substrates enclosing the fiber optic deviceand the deformable metal interface layer. Hence, the metal seals providean interface for an enclosure, enabling the desired mechanical state ofa fiber optic device to be preserved in order to maintain the desiredoptical characteristics. In addition, the metal seals enable anenclosure to maintain the operating environment of the desired opticaldevice, for example an inert gas having a predetermined refractiveindex. The use of metal seals also ensures that the desired opticalcharacteristics of the fiber optic device are protected from adverseenvironmental effects, including shock, contamination due to oxygen,water vapor, etc. to the extent that the fiber optic device ishermetically sealed in a gas-tight enclosure. Finally, the disclosedembodiments provide an arrangement where the long-term reliability andintegrity of the first gas-tight enclosure is maintained by protectingthe first gas-tight enclosure within a second gas-tight enclosure.Hence, an optical fiber device may be hermetically sealed in anefficient manner to preserve its desired optical characteristics. Theindustry-acceptable leak rate for hermetic packages is less than 5×10⁻⁸Std. CC atm/min. It is believed the disclosed embodiments satisfy thisindustry standard.

According to the present invention, metal seals are used to preserve thedesired optical characteristics of a fiber optic device. Although thedisclosed embodiments use substrates having metal layers, it will beappreciated that the metal layers may be added to quartz substrates. Forexample, the fiber optic device may be placed within an enclosureconsisting essentially of fused quartz. Metal may then be added to thesurfaces of the quartz substrate, including at the end portionsreceiving the optical fibers. A complementary quartz substrate wouldthen be placed on top of the first substrate having the added metal, andadditional metal would be added to seal the fiber optic device withinthe quartz substrates. In such an arrangement, the desired opticalcharacteristics of a fiber optic device may be preserved by adding themetal to the quartz substrates.

In addition, the present invention is not limited to protecting fiberoptic devices having a plurality of optical fibers. Rather, thedisclosed embodiments may be used to protect other fiber optic devices,for example a laser diode, at the end of a single optical fiber.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not limited to thedisclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

I claim:
 1. An apparatus comprising:a fiber optic device comprising atleast one optical fiber having an exposed region; first and second metalseals surrounding the optical fibers at respective first and secondlocations of the exposed region; a first enclosure sealing the fiberoptic device between the first and second metal seals, the firstenclosure comprising:(1) a first substrate having a middle inner surfaceand end surfaces, the end surfaces contacting first surfaces of thefirst and second metal seals, respectively, and (2) a second substratehaving a middle inner surface contacting the corresponding middle innersurface of the first substrate and end surfaces contacting secondsurfaces of the first and second metal seals, respectively, and themiddle and end surfaces of the first and second substrates.
 2. Theapparatus of claim 1, further comprising a sleeve surrounding the firstenclosure and compressing the first and second substrates.
 3. Theapparatus of claim 2, wherein the first and second substrates eachfurther comprise an outer surface, and a metal layer overlying thecorresponding middle inner, end, and outer surfaces.
 4. The apparatus ofclaim 3, wherein the sleeve, the metal layers, and the metal sealsconsist essentially of pure aluminum, the sleeve and the metal layeroverlying the outer surface sealing the first enclosure.
 5. Theapparatus of claim 4, wherein the sleeve and the metal layer overlyingthe outer surface hermetically sealing the first enclosure.
 6. Theapparatus of claim 1, wherein the first and second substrates eachcomprise fused silica and a metal layer overlying at least a portion ofthe fused silica.
 7. The apparatus of claim 1, wherein the firstenclosure encloses an inert gas at a predetermined pressure.
 8. Theapparatus of claim 7, wherein the inert gas is one of nitrogen, heliumand argon.
 9. The apparatus of claim 8, wherein the predeterminedpressure is greater than ambient air pressure.
 10. The apparatus ofclaim 1, wherein the first substrate and the second substrate eachcomprise a trough accommodating the fiber optic device.
 11. Theapparatus of claim 1, wherein said first and second substrates eachcomprise fused silica and a metal layer overlying at least a portion ofthe fused silica.
 12. The apparatus of claim 1, wherein the metal sealsform a chemical bond with the exposed optical fiber at the first andsecond locations, respectively.
 13. The apparatus of claim 1, whereinthe first and second substrates each have a center section and endportions having a smaller outside diameter than the center section. 14.The apparatus of claim 1, wherein the metal seals provide stress reliefbetween the at least one optical fiber and the enclosure.
 15. Anapparatus comprising:a fiber optic device comprising at least oneoptical fiber having an exposed region; a first enclosure including afirst substrate and a second substrate and enclosing said fiber opticdevice and a portion of said exposed region of said optical fiber, saidfirst and second substrates having at least one end region through whichsaid exposed region of said optical fiber extends; said first enclosureincluding a metal seal sealing the fiber optic device within said firstand second substrates at the end region wherein the metal seal is formedfrom a metal layer overlying at least a portion of each of the first andsecond substrates and secured to the optical fiber.
 16. The apparatus ofclaim 15, further comprising a sleeve surrounding and compressing thefirst enclosure.
 17. The apparatus of claim 15, wherein said sleeve andsaid metal seal consist essentially of pure aluminum.
 18. The apparatusof claim 15, wherein the first and second substrates comprise fusedsilica.
 19. The apparatus of claim 15, wherein the metal seal ishermatic seal.
 20. The apparatus of claim 15, wherein the firstenclosure encloses an inert gas at a predetermined pressure.
 21. Theapparatus of claim 20, wherein the inert gas is one of nitrogen, heliumand argon.
 22. The apparatus of claim 20, wherein the predeterminedpressure is greater than ambient air pressure.
 23. The apparatus ofclaim 15, wherein the metal seal forms a chemical bond with the exposedoptical fiber at first and second locations, respectively.